Stator laminations for rotary actuator

ABSTRACT

A rotary actuator includes an outer enclosure having an inner diameter surrounding a hollow interior. A stack of stator laminations, each having a stator diameter greater than the inner diameter of the outer enclosure when in an unflexed state, are also included in the rotary actuator. Each of the stator laminations is configured to flex into a shape so as to be positionable within the outer enclosure and substantially conform to the inner diameter. The stator lamination thus forms a line-to-line fit with at least a portion of the outer enclosure to form an interface having a desirable reluctance.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of, and claims priority to, U.S.application Ser. No. 11/861,147 filed Sep. 25, 2007, the disclosure ofwhich is incorporated herein by reference, and which further claimed thebenefit of prior U.S. Provisional Application No. 60/969,045, filed onAug. 30, 2007.

BACKGROUND OF THE INVENTION

The present invention relates generally to electromagnetic actuators,and more particularly, to a stator lamination and outer housing of anactuator.

The desirability of and need for a rotary electromagnetic actuators hasbeen recognized for years. A factor in the effectiveness of rotaryelectromagnetic actuators is the ability of the actuator to convertelectromagnetic forces into useful output torque. That is, theefficiency of the actuator in converting electromagnetic forces intouseful output torque is of primary importance. In some rotary actuatordesigns, a significant factor in this conversion is the presence ofundesired air gaps in the actuator, and more specifically, the presenceof air gaps between an outer enclosure and a stator in the actuator. Forrotary actuators in which a magnetic flux path is formed by a rotor, astator lamination stack, and an outer enclosure, such undesired air gapsgreatly reduce the torque output of the actuator and lead to significantinefficiency in converting electromagnetic forces into useful outputtorque by creating undesirable reluctance. Useful output torque ismaximized when the stator-armature gap provides a flux path having aminimal reluctance.

In an effort to minimize or eliminate this undesirable air gap, theinterface between the stator lamination stack and an inner surface ofthe outer housing needs to be a precision line-to-line fit to eliminatea performance-reducing air gap. In an effort to form this line-to-linefit, current technology relies on a method to heat outer enclosure toexpand its inner diameter in order to press the stator lamination intothe enclosure. That is, the outer circular enclosure is heated to adesired temperature, and then the stator lamination stack is pressedinto the outer enclosure. As the outer enclosure cools, it creates apress fit between the two parts. Such a process, however, is complex andcostly, and additionally, may not always form an adequate line-to-linefit at desired locations in the actuator so as to form an efficient fluxpath.

In another commonly used method, the outer enclosure is made from sheetmetal that is wrapped around the stator lamination stack. An additionaladhesive may be employed to form a solid connection between the outerenclosure and the stator laminations to prevent unwanted rotation oraxial translation therebetween. However, such an adhesive can functionas an undesirable air gap and increase reluctance. Furthermore,application of the outer enclosure in such a manner results in a seamwithin the enclosure, which leaves the actuator unsealed.

Therefore, a need exists for a stator lamination design and method ofpositioning the stator lamination within an outer enclosure is efficientand cost effective. Additionally, it is desired that such a statorlamination design and construction method assures a line-to-line fitbetween the stator lamination stack and outer enclosure so as toeliminate a performance reducing air gap therebetween and form anefficient magnetic flux path.

BRIEF DESCRIPTION OF THE INVENTION

The present invention overcomes the aforementioned problems by providinga system and method of forming and positioning a stator laminationwithin an outer enclosure of a rotary actuator. A flexible statorlamination is designed to deform when pressure is applied thereto, thusallowing the stator lamination to be positioned within the outerenclosure.

In accordance with one aspect of the invention, a rotary actuatorincludes an outer enclosure having an inner diameter surrounding ahollow interior and a stack of stator laminations, with each of thestator laminations, when in an unflexed state, have a stator diametergreater than the inner diameter of the outer enclosure. Each of thestator laminations is configured to flex into a shape so as to bepositionable within the outer enclosure and substantially conform to theinner diameter.

In accordance with another aspect of the invention, an electric motorincludes a housing tube, a plurality of stator laminations positionablewithin an inner circumference of the housing tube when the plurality ofstator laminations are in a compressed state, and a rotor positionedadjacent to the plurality of stator laminations and configured to rotaterelative to the plurality of stator laminations. Each of the statorlaminations has a first diameter that is greater than an inner diameterof the housing tube when in an uncompressed state.

In accordance with yet another aspect of the invention, a method formanufacturing a rotary actuator includes the step of constructing aplurality of elliptical stator laminations, with each of the ellipticalstator laminations having a first diameter and a second diameter in anunflexed state and wherein the first diameter is greater than the seconddiameter. The method also includes the steps of constructing a tubeshaped housing having a circular diameter less than the first diameterand greater than the second diameter and flexing the elliptical statorlaminations to decrease a size of the first diameter such that it isless than the circular diameter. The method further includes the stepsof positioning the flexed elliptical stator lamination within the tubeshaped housing and forming a press fit between the elliptical statorlamination and the tube shaped housing at a plurality of pre-determinedlocations on the elliptical stator lamination.

Various other features and advantages of the present invention will bemade apparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout the invention.

In the drawings:

FIG. 1 is a cross-sectional view of a rotary actuator according to anembodiment of the present invention.

FIG. 2 is an end view of a stator lamination and outer enclosure useablewith the rotary actuator of FIG. 1 according to one embodiment of thepresent invention.

FIG. 3 is an end view of the stator lamination and outer enclosure ofFIG. 2 with the stator lamination positioned within the outer enclosure.

FIG. 4 is an end view of a stator lamination and outer enclosure useablewith the rotary actuator of FIG. 1 according to another embodiment ofthe present invention.

FIG. 5 is an end view of the stator lamination of FIG. 4 in a fullyflexed or compressed state.

FIG. 6 is an end view of the stator lamination and outer enclosure ofFIG. 4 with the stator lamination positioned within the outer enclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an electromagnetic motor 10 is shown as an actuatorof the “rotational” type, wherein a rotor 12 swings about an axisrelative to a stator 14 as the excitation of an associatedelectromagnetic coil is varied. In the preferred embodiment, the rotaryactuator 10 is illustrated as a limited angle torquer (LAT) whichconverts an input current to a proportionally related rotary outputposition of an output shaft 16. As its principal components, theactuator includes a stator assembly 16 associated with a rotor assembly14 journaled or pivoted to swing about an axis relative to the stator16, so that a working gap 18 is maintained between the two components toform part of a magnetic flux path 20. A coil assembly 22 is disposedwithin the rotary actuator 10 to create an excitation current. Theexcitation current creates a magnetomotive force (m.m.f.) to drivemagnetic flux in the closed magnetic flux path 20 which includes the gap18. Such magnetic flux attracts the rotor 14 toward the stator 16,according to well known principles of magnetism, and tends thus to urgethe rotor either clockwise or counterclockwise to create a workingtorque output.

The rotary actuator 10 also includes an outer enclosure 24 (i.e.,housing tube) having a hollow interior. The outer enclosure 24 housesthe stator assembly 16 and rotor assembly 14 therein. Outer enclosure 24is formed of a metallic material (e.g., steel) having a desirablemagnetic reluctance value so as to form part of magnetic flux path 20.Outer enclosure 24 also functions to effectively seal off the statorassembly 14 and rotor assembly 14 from the ambient environment.

Referring now to FIG. 2, a stator lamination 26 is shown in an unflexedstate and alongside outer enclosure 24. A plurality of statorlaminations 26, in summation, form the stator assembly 16 of rotaryactuator 10 (as shown in FIG. 1) when positioned within outer enclosure24. As shown in FIG. 2, stator lamination 26 is of a generallyelliptical or oblong shape. The stator lamination 26 thus is configuredto have a first diameter 28 and a second diameter 30. In an unflexedstate, first diameter 28 is greater than second diameter 30. Incomparison to an inner circular diameter 32 of outer enclosure 24, firstdiameter 28 is larger than circular diameter 32 and second diameter 30is less than circular diameter 32.

At the portions of stator lamination 26 that correspond to firstdiameter 28, pole faces 34 are formed on the stator lamination 26. Atthe portions of stator lamination 26 that correspond to second diameter30, non-active faces 36 that are not part of a flux path between outerenclosure 24 and stator laminations 26 are formed thereon. The width ofthe stator lamination 26 at the non-active faces 36 in the direction ofsecond diameter 30 is less than the thickness of the stator lamination26 at the pole faces 34 in the direction of first diameter 28. As such,stator lamination 26 is constructed to flex and deform along thenon-active faces 36, thus increasing a length of second diameter 30 anddecreasing a length of first diameter 28.

Referring now to FIG. 3, stator lamination 26 is shown in a flexed stateand positioned within outer enclosure 24. As a pressure is applied toopposite ends of stator lamination 26 at the pole faces 34, the lengthof first diameter 28 is decreased to a length less than or equal to thatof circular diameter 32. The length of second diameter 30 is increasedduring such flexing, but the length of second diameter 30 remains lessthan the length of circular diameter 32, even when stator lamination 26reaches a maximum flexed state. After stator lamination 26 has beenflexed to a point at which each of the first and second diameters 28, 30are less than or equal to circular diameter 32, stator lamination 26 ispositioned within outer enclosure 24. Upon placement within outerenclosure 24, stator lamination 26 attempts to deform from its flexedstate back to its original unflexed state, as is shown in FIG. 2.However, the dimensions of outer enclosure 24 (i.e., circular diameter32) prevent stator laminations 26 from returning to this original,unflexed state. Thus, stator lamination 26 deforms to an intermediatestate at which the stator lamination 26 conforms to outer enclosure 24at a number of pre-determined locations/points. That is, statorlamination 26 forms a line-to-line fit with outer enclosure 24 at eachof the pole faces 34 on stator lamination 24. At the interface betweenthe pole faces 34 and the outer enclosure 24, no air gap is present,thus providing for an improved flux path between the stator lamination26 and the outer enclosure 24 as compared to if a void (i.e., undesiredair gap) were present between the two components. In addition toeliminating the presence of an air gap, the line-to-line fit betweenstator lamination 26 and outer enclosure 24 also forms a press fit thatprevents rotation and axial translation of stator lamination 26 relativeto outer enclosure 24.

While a line-to-line fit between stator lamination 26 and outerenclosure 24 is formed at each of pole faces 34 in the intermediatestate, non-active faces 36 remain spaced apart from outer enclosure 24.This spacing or presence of a void 38 between non-active faces 36 andouter enclosure 24 allows the stator lamination 26 to maintain aspring-like effect. That is, non-active faces 36 continue to apply anoutward pressure directed toward pole faces 34 to form the press fitbetween pole faces 34 and outer enclosure 24. The desire of statorlamination 26 to return to its original size and shape generates a gripon the inner circular diameter 32 of outer enclosure 24 that holds thestator lamination 26 in place, thus eliminating any need for anadditional adhesive or feature to prevent unwanted rotation or axialtranslation of the stator laminations 26.

The spring-like effect of stator lamination 26 between its flexed andunflexed states allows its oversized first diameter 28 to vary in sizeto closely fit the circular diameter 32 of outer enclosure 24 throughoutthe enclosure's tolerance range. That is, the pole faces 34 that formthe critical flux path 20 (shown in FIG. 1) between stator lamination 26and outer enclosure 24 are compressed to conform to the outer enclosure24, regardless of a variation in the circular diameter 32 of outerenclosure 24. Thus, issues caused by imprecise tolerances of the outerenclosure circular diameter 32 can be prevented, as the spring-likeeffect of stator lamination 26 ensures a precise, line-to-line fitbetween the stator lamination 26 and the outer enclosure circulardiameter 32.

In another embodiment shown in FIG. 4, a stator lamination 40 isconfigured as a circular lamination having a break 42 therein. That is,circular lamination 40 has a first end 44 and second end 46 with a gap42 formed therebetween. The gap 42 is formed so as to allow for aflexing of the circular lamination 40 when pressure is applied thereto.Hooks 48 are provided at each of the first and second ends 44, 46 toform an abutment surface 50 that prevents the first and second ends 44,46 from sliding past one another when the circular lamination 40 isflexed.

As shown in FIG. 4, in an unflexed state, a circular or stator diameter52 of stator lamination 40 is greater than the inner circular diameter32 of outer enclosure 24. Thus, in order to position circular lamination40 within outer enclosure 24, a pressure is applied to circularlamination 40 to decrease the size of the gap 42 between the first andsecond ends 44, 46 of the circular lamination. As the size of gap 42 isdecreased, the size of the stator diameter 52 is also decreased. Thus,stator diameter 52 is variable depending on the state of flex of statorlamination 40.

Referring now to FIG. 5, in a fully flexed state, where first and secondends 44, 46 of circular lamination abut one another on abutment surface50, the stator diameter 52 is less than or equal to circular diameter 32of outer enclosure 24 such that circular lamination 40 is configured forpositioning within outer enclosure 24.

As shown in FIG. 6, after positioning circular lamination 40 withinouter enclosure 24, circular lamination 40 is allowed to deform from itsmaximum flexed state back toward its original unflexed state (shown inFIG. 4). As circular lamination 40 begins to conform to an innercircumference of outer enclosure 24, circular lamination 40 reaches anintermediate state that results in a stator diameter 52 between that ofthe diameter in the original unflexed state and that of the maximumflexed state. The force created by the desire of circular lamination 40to return to its original unflexed state creates a press fit between thecircular lamination 40 and the outer enclosure 24, thus preventingrotation and axial translation between the two components. As shown inFIG. 6, this spring-like force also assures the existence of aline-to-line fit between the circular lamination 40 and outer enclosure24, which eliminates any undesired air gaps therebetween that couldreduce performance of the rotary actuator 10 by increasing a reluctancein the critical flux path 20 (see FIG. 1).

Therefore, according to one embodiment of the present invention, arotary actuator includes an outer enclosure having an inner diametersurrounding a hollow interior and a stack of stator laminations, witheach of the stator laminations, when in an unflexed state, have a statordiameter greater than the inner diameter of the outer enclosure. Each ofthe stator laminations is configured to flex into a shape so as to bepositionable within the outer enclosure and substantially conform to theinner diameter.

According to another embodiment of the present invention, an electricmotor includes a housing tube, a plurality of stator laminationspositionable within an inner circumference of the housing tube when theplurality of stator laminations are in a compressed state, and a rotorpositioned adjacent to the plurality of stator laminations andconfigured to rotate relative to the plurality of stator laminations.Each of the stator laminations has a first diameter that is greater thanan inner diameter of the housing tube when in an uncompressed state.

According to yet another embodiment of the present invention, a methodfor manufacturing a rotary actuator includes the step of constructing aplurality of elliptical stator laminations, with each of the ellipticalstator laminations having a first diameter and a second diameter in anunflexed state and wherein the first diameter is greater than the seconddiameter. The method also includes the steps of constructing a tubeshaped housing having a circular diameter less than the first diameterand greater than the second diameter and flexing the elliptical statorlaminations to decrease a size of the first diameter such that it isless than the circular diameter. The method further includes the stepsof positioning the flexed elliptical stator lamination within the tubeshaped housing and forming a press fit between the elliptical statorlamination and the tube shaped housing at a plurality of pre-determinedlocations on the elliptical stator lamination.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A method for manufacturing a rotary actuator comprising: constructinga plurality of elliptical stator laminations, each of the ellipticalstator laminations having a first diameter and a second diameter,wherein, in an unflexed state, the first diameter is greater than thesecond diameter; constructing a tube shaped housing having a circulardiameter less than the first diameter and greater than the seconddiameter; flexing the elliptical stator laminations to decrease a sizeof the first diameter such that it is less than the circular diameter;positioning the flexed elliptical stator lamination within the tubeshaped housing; and forming a press fit between the elliptical statorlamination and the tube shaped housing at a plurality of pre-determinedlocations on the elliptical stator lamination.
 2. The method of claim 1wherein the step of constructing the plurality of elliptical statorlaminations comprises: forming a pair of inflexible pole faces; forminga pair of flexible wall sections; and wherein the pair of inflexiblepole faces defines the first diameter of the elliptical statorlamination and the pair of flexible wall sections defines the seconddiameter of the elliptical stator lamination.
 3. The method of claim 2wherein the press fit between each elliptical stator lamination and thetube shaped housing forms a magnetic flux path between the pole facesand the tube shaped housing.
 4. The method of claim 2 wherein the stepof forming a press fit further comprises creating a line-to-line fitbetween the inflexible pole faces and the tube shaped housing as theelliptical stator lamination transitions from the flexed state to anintermediate state.
 5. The method of claim 4 wherein the second diameteris further less than the circular diameter in the intermediate state. 6.The method of claim 1 wherein an interface between the elliptical statorlamination and the tube shaped housing is free of an adhesive.
 7. Themethod of claim 1 further comprising releasing the elliptical statorlamination upon its positioning within the tube shaped housing, suchthat the press fit between the elliptical stator lamination and the tubeshaped housing is formed at the plurality of pre-determined locations.8. The method of claim 7 wherein the elliptical stator laminationsubstantially conforms to the tube shaped housing upon the releasethereof.
 9. The method of claim 1 wherein the second diameter of theelliptical stator lamination is less than the circular diameter of thetube shaped housing in the unflexed state.
 10. The method of claim 1wherein the press fit between each elliptical stator lamination and thetube shaped housing prevents rotation and axial translationtherebetween.
 11. A method for manufacturing a rotary actuatorcomprising: constructing a plurality of stator laminations, each of thestator laminations comprising a flexible stator lamination having afirst diameter and a second diameter, wherein, in an unflexed state, thefirst diameter is greater than the second diameter; constructing a tubeshaped housing having a circular diameter less than the first diameterand greater than the second diameter; flexing the stator laminations toa flexed state so as to decrease a size of the first diameter such thatit is less than the circular diameter; positioning the flexed statorlamination within the tube shaped housing; releasing the statorlamination such that it transitions from the flexed state to anintermediate state, the intermediate state comprising a state of flexbetween the unflexed state and the flexed state; forming a press fitbetween the stator lamination and the tube shaped housing at a pluralityof pre-determined locations on the stator lamination with the statorlamination in the intermediate state.
 12. The electric motor of claim 11wherein constructing the plurality of stator laminations comprises:forming a pair of inflexible pole faces; forming a pair of flexible wallsections; and wherein the pair of inflexible pole faces defines thefirst diameter of the stator lamination and the pair of flexible wallsections defines the second diameter of the stator lamination.
 13. Theelectric motor of claim 12 wherein the press fit between each statorlamination and the tube shaped housing forms a magnetic flux pathbetween the pole faces and the tube shaped housing.
 14. The electricmotor of claim 11 wherein the press fit between the stator laminationand the tube shaped housing is free of an adhesive therebetween
 15. Theelectric motor of claim 11 wherein the press fit between each statorlamination and the tube shaped housing prevents rotation and axialtranslation therebetween.
 16. The electric motor of claim 11 wherein thesecond diameter of the stator lamination is less than the circulardiameter of the tube shaped housing in the unflexed state.
 17. A methodfor manufacturing a rotary actuator comprising: constructing a pluralityof stator laminations, each of the stator laminations comprising acircular lamination having a first end and a second end separated by agap therebetween, the circular lamination having a first diameter whenin an unflexed state; constructing a tube shaped housing having acircular diameter less than the first diameter; flexing the statorlaminations to decrease a size of the gap between the first end and thesecond end and such that the diameter of the circular lamination isdecreased from the first diameter to a second diameter that that is lessthan the circular diameter of the tube shaped housing; positioning theflexed stator lamination within the tube shaped housing; and releasingthe stator lamination to form a press fit between the stator laminationand the tube shaped housing.
 18. The method of claim 17 wherein each ofthe first and second ends of the stator lamination further comprises ahook formed thereon to form an abutment surface.
 19. The method of claim17 wherein the step of constructing the plurality of stator laminationscomprises forming a pair of pole faces on each stator lamination. 20.The method of claim 19 wherein the pole faces form a press fit with thetube shaped housing when the stator lamination is positioned andreleased within the tube shaped housing.